Process for gelling frothed rubber latices on fabrics



COMPOUND AND FROTH LATEX BY STEAM CURE AND DRY GELLED LATEX BACKING FIG! F. G. CALLAHAN GELL FROTH LATEX ON GELLED LATEX Filed Feb. 3. 1965 EMBOSS DESIGN APPLY FROTH LATEX TO BACK OF CARPETv PROCESS FOR GELLING FROTHED RUBBER LATICES ON FABRICS Oct. 25, 1966 Iii/,2

STEAM INVENTOR FRANCIS G. CALLAHAN BKM ATTORNEYS IIIIIIIIIIAS 7111,!!!

CONDENSATE United States Patent Office 3,281,258 Patented Oct. 25, 1966 PROCESS FOR GELLING FROTHED RUBBER LATICES N FABRICS Francis G. Callahan, Dalton, Ga., assignor to Textile Rubber and Chemical Company, Inc., Dalton, Ga., a corporation of Georgia Filed Feb. 3, 1965, Ser. No. 430,041 Claims. (Cl. 11710) My invention relates to an improved method of gelling latex coated fabrics such as carpets and rugs. In particular, my method concerns the gelling by steam of a frothed latex back-coated carpet or rug and the subsequent embossing of the stiffened frothed latex with a suitable design thereby providing a cellular or sponge latex back-coated carpet or rug.

In the preparation of sponge or cellular elastomer backings for fabrics such as carpets and rugs, a latex is typically frothed to a desired density by mechanical or chemical means and then spread to a pedetermined depth on the back of a carpet or other support web. This frothed latex coating is then gelled or stiffened by the application of heat, such as by passing the coated carpet under radiant heaters or through a warm air oven at the desired temperatures. The stiffened latex is then compacted to the desired density and embossed with a particular design. Embossing and compacting is usually accomplished by passing the carpet between squeeze rolls with the roll in contact with the gelled latex backing usually engraved or cut to provide a design in the compacted, gelled, frothed back-coating. The embossed latex coated carpet is then dried and cured in the usual manner such as by passing through a warm air oven to provide a carpet having a cellular or sponge, latex designed, backing securely bonded to the carpet. In some applications, a pre-coat is used on the back of the carpet to aid in anchoring the frothed latex backing to the carpet.

In the gelling operation, it is customary to pass a froth-coated carpet through a long gelling oven which contains a series of infra-red radiant heaters directed at the froth and, in some instances, below the carpet and directed upwardly to the face of the carpet. Considerable heat is required in the gelling operation in order to completely and adequately gell the thickly coated frothed latex from the upper surface of the froth down to the froth in contact with the carpet. satisfactorily embossing results when the froth is evenly gelled and gelled substantially all the way through the frothed layer. Radiant heaters have proven somewhat unsatisfactory for the gelling operation since these heaters often tend to overheat the frothed surface before the interior of the coating is properly gelled. When the frothed surface is too dry or cured in any way, this results in a poor embossing design due to the firmness of the surface of the gelled froth. Ungelled froth at the bottom of an incompletely gelled layer on the carpet often causes trouble during the embossing step by being squeezed back from the area of the nip and can result in the accumulation of ungelled froth in the form of a balloon between the carpet and the gelled surface of the frothed layer. This accumulation of ungelled froth can also cause trouble when it breaks through the surface of the gelled froth and also causes distortion of the gelled fro-th as it is being compacted and squeezed against the carpet back. Additionally, radiant heat direct against the fabric carpet face, such as for example, a tufted carpet face, can be a potential fire hazard should lint fall from the carpet face and onto the hot surface of the glowing radiant heaters. To overcome the aforementioned disadvantages, proper gellation of the frothed latex is accomplished by the employment of a long, warm air tunnel or oven following the application of radiant heat. However, this arrangement requires the installation of an additional drying oven and requires additional space for the processing operation.

It is an object of my invention to provide a method of overcoming many of the disadvantages of the present methods of gelling a latex coating on a porous support web. It is also an object of my invention to provide a simple and inexpensive means for rapidly gelling a frothed latex back-coating on carpets and rugs. Other objects and advantages of my invention will be apparent to those skilled in the art from the following descrip tion of my discovery taken in conjunction with the drawing wherein:

FIGURE 1 is the stepwise flow diagram of my method of fabricating an embossed sponge rubber backed carpet.

FIGURE 2 is a fragmentary schematic illustration of the gelling and embossing steps of my method.

I have found that a frothed lat-ex may be properly and rapidly gelled by the direct application of steam to the bottom of a froth-coated carpet. The application of wet steam directed upwardly against the carpet face permits a rapid gellation of the frothed latex to proceed upwardly from the back surface of the carpet to the top of the frothed layer and avoids the previous difficulties encountered by the formation of dry and overheated surface skin of the frothed latex. The rapid and progressive gellation upwardly from the back surface of the carpet also permits enhanced results to be attained in the embossing step and avoids the fire hazards of employing radiant heaters against the carpet face. Further, the use of wet steam promotes the rapid transfer of heat into the carpet and frothed latex by the heat of the steam and by the latent heat of condensation of the steam. Accordingly, my invention not only avoids many of the difiiculties associated with the past practices of gellation, but also is a simple and inexpensive method of gellation. By my method, the gellation is extremely rapid with the froth gelling quickly in the layer against the back surface of the carpet. The surface above the carpet accordingly gells more slowly and is more receptive to the embossing than when heated for a rather long time with radiant heaters. The use of live steam in my method permits a substantial shortening of the gelling area, improves the plasticity of the gelled froth to aid in easy embossing with a lower pressure being needed at the squeeze rolls and provides for higher processing speed.

In one prferred embodiment of my invention, steam is directed upwardly against the ungelled latex froth by the use of a steam box constructed to fit under the carpet with one open side in contact with the carpet face so that the carpet actually contacts the upper walls of the steam box and prevents the steam from escaping except upwardly through the carpet fabric and into the frothed latex.

An open top steam box running the width of the carpet is particularly useful when a continuous width carpet is being steamed. A covered perforated top steam box may also be used. A perforated top steam box finds particular usefulness when coated strips running side by side are to be steamed in the manner described. A steam box with a top cover perforated with A holes spaced about /2" apart in staggered rows gives excellent results with coated strip material. A slight positive pressure within the steam box allows steam to be forced upwardly into the coated goods even though the top of the box is not completely covered with strips. Several parallel steam pipes perforated with suitable staggered rows of holes will also provide steam to the bottom of a coated carpet passed over the pipes.

Steam may also be applied against the carpet face upsired body to the formulation.

wardly by the use of jets or slots in steam pipes in contact with or just slightly below the face surface of the carpet, or by any other means of applying steam directly to the face of the carpet. The use of steam applied to the face of a carpet may also be accompanied by limited and supplemental heating means such as the use of conventional radiant heaters or steam directed downwardly toward the surface of the frothed latex or the use of a conventional warm air oven. Very fast gellation is obtained by using a limited amount of radiant heat directed downwardly towards the Wet frothed latex together with the application of wet steam upwardly to the face of the carpet.

A typical method of preparing a cured cellular latexbacked tufted carpet is schematically illustrated in FIG- URE l. A gellable and curable natural or synthetic elastomer or other polymeric latex solution is compounded with the desired additives such as curing and accelerating agents, dyes, fillers, pigments, antioxidants, stabilizers, thickeners, stiffening agents, gelling agents and the like. Suitable natural and synthetic elastomers which may be employed in the practice of my invention, include but are not limited to, those rubbery copolymers of styrene and butadiene (SBR), acrylonitrile-diene copolymers such as acrylonitrile-butadiene and acrylonitrile-butadienestyrene copolymers, natural rubbers, polybutadiene, polyisoprene, halogenated dienes likefchloroprene, butyl rubber and the like as well as other gellable and heat curable polymeric latices containing polyolefins, acrylates and the like. Particularly useful latices for preparing rug and carpet backings, include natural rubber and SBR and mixtures thereof as well as carboxylated latices, such as carboxylated SBR, carboxylated Buna N and the like. Carboxylated latices may be employed where it is desired to obtain both cross-linking and gelling by the use of heat and cross-linking additives through the latex.

A typical formulation useful in providing a skid-resistant latex back-coating for a tufted carpet or rug is as follows:

Dry weight in Although some latices may be gelled by the application of heat alone, it is often useful and preferred to incorporate into the latices a gelling agent in an amount sufficient to aid in the stiffening and gelling of the latex when subject to heat. With anionic latex formulations an acid or acid salt is often used as a gelling agent. Typical acid salts would include ammonium acetate, ammonium chloride, ammonium sulfate, sodium sili-cofluoride and other acid salts. In preparing a frothed or foamed latex coating, it is often desirable to incorporate into the formulation stiffening agents, such as polyvinyl acetate in emulsion form in an amount sufficient to impart the de- Additionally, thickeners Such as polyvinyl pyrilidone, polyvinylalcohol, polyacrylates and the like may also be employed.

The latex is then frothed to a desired degree of density by rapid agitation and mechanical stirring to incorporate air therein, such as to a density of from about 250 to 600 grams per liter. One method of preparing a frothed I or foamed latex is to pump a latex solution into a machine and to inject air into the latex solution from a flow meter controlling the amount and pressure of the air thereby providing a uniform blend in a mixing chamber of air which is finely divided throughout the latex solution. The air frothed latex is then applied by a knifeor barcoater or other coating techniques including application from a roller coater to the back surface of a tufted carpet. The coating weight of the frothed latex employed may vary widely depending upon the type and character of the surface ultimately desired; however, in preparing skid-resistant carpets, a coating weight of 20 to 40 ounces per square yard of carpet is often employed with the depth of the frothed latex ranging from about /s to A of an inch. If desired, a thin coating of a pre-coating latex solution may be applied to the back surface of the carpet prior to the application of the frothed latex to enhance the bonding and adhesion of the final cured frothed latex coating to the carpet. A suitable pre-coat formulation would include a mixture of a carboxylated latex with a natural rubber latex blend highly loaded with from about 300 to 800 parts per parts of elastomer with a filler. After the application of the frothed latex layer to the carpet back, the carpet is moved into a chamber wherein a gelling operation is carried out. The frothed latex backcoating is progressively and rapidly gelled upwardly from the back surface of the carpet to the top of the frothed latex surface by the application of steam to the carpet face. To provide rapid gellation, the steam must penetrate the face of the carpet or fabric and move upwardly into the frothed latex coating. In the gellation step, sufficient heat is employed, for example, 200 to 240 F. to obtain gellation of the frothed latex but insufficient to cure the frothed latex. In my invention, gellation is accomplished by applying wet steam directly across the full width of the carpet and to the bottom of the carpet.

FIGURE 2. is a fragmentary schematic view of the gelling and embossing operation of my method. The carpet 10 composed of a woven backing fabric 12 and having a plurality of V or tuft fibres 14 sittched therethrough to form a tufted carpet face downwardly disposed as the back surface thereof is coated with a frothed latex layer 16. The back-coated carpet is moved forward over support rollers 18 and 20 between which rollers is located an enclosed steam box 22 within a heating chamber or oven 24. The steam box is open at the top and extends across the full width of the carpet in the direction of travel of the carpet. The tops of the sidewalls of the rectangular steam box 22 are norm-ally placed in contact with the face of the carpet 10. Steam is introduced under slight pressure into the steam box and permitted to pass only upwardly against and through the carpet face to gell the latex layer 16. I have found it profitable to employ sufficient steam pressure to how the carpet slightly upward .over the open area of the steam box 22. A typical tufted carpet coated as described having about 12 feet in width and run at a speed of 12 feet per minute will provide for rapid gellation of the frothed latex back coating when the open top of the steam box is from one to three feet in width across the width of the carpet and steam equivalent to a 5 to 10 H1. boiler is employed. In general, the steam pressure used should be insuflicient to lift the carpet from the edges of the box since this would tend to permit steam to escape. Within the chamber 24 is also a black panel radiant electric heater 26 used to direct a slight amount of radiant heat downwardly onto the surface of the frothed la-tex. The use of a downwardly directed heating operation in combination with the open steam box 22 aids in rapid gellation and uniform gellation of the coating layer, but is not essential in carrying out the features of my invention. In a typical operation, a speed of 12 feet per minute may be used with a steam box of about two feet in length in the direction of the travel of the carpet and with about six feet of overhead radiant heaters. In this combination gellation is obtained in about to 20 seconds without the formation of a dry surface skin. A conventional radiant .oven employed under similar conditions usually exceeds thirty feet in length and does not permit speeds as high as 10 to 12 feet per minute.

After proper gellation to the desired degree of stiffness, the gelled or stiffened frothed latex layer is embossed and compacted. An embossing depth from about to A of an inch is often employed to obtain a desired design on the back-coating. The gelled back-coating may be embossed by passing it between an engraved top embossing roller 28 and a smooth bottom roller 30. These rollers, 28 and 30, may be heated or if sticking is a problem, may be unheated rollers located either within the chamber 24 or without the chamber 24. In one preferred application, the engraved embossing roller 28 imparts a waffle or grid-like design onto the stiffened latex frothed back-coating to provide a rug or carpet enhanced skidresistant propertie as shown. The embossed back design as shown is characterized by a plurality of thin, rounded, grid-like projections or ribs in a square, rectangular, diamond or like design. The rounded projections 32 are designed to be placed in contact with the floor surface and to impart skid-resistant properties to the rub. The ribs or projections 32 are about to M inch in depth and are usually spaced a quarter inch or more apart or less than about A1, of the width of the intervening compacted spaces 34. This design permits the back-coating to possess a good cushioning property to the carpet. The waflle-like design coupled with the cellular nature of the backing and the entrapment of air in the intervening spaces between the rib provides a skid-resistant carpet having good cushioning effects. The uniform and rapid gellation of the frothed latex permitted by my discovery permits lower embossing pressures of about 5 to 15 pounds per inch of carpet width to be used, for example 5 to 12 pounds per inch of carpet width. The lower embossing pressure is accomplished because of the improved plasticity of the uniformly gelled froth by my rapid gellation method.

My method permits the gelled fioth to be squeezed during the embossing operation with suflicient pressure to effect removal of all, substantially all, or a desired high portion of the entrained air, thus providing a firm, relatively thick solid latex backing having greater strength and scufi resistance than conventional low density or sponge rubber. The embossed gelled back-coating 16 is then cured and dried in a conventional warm-air oven such as at the temperature of about 250 to 450 -F. for 5 to 15 minutes, e.g. 325 F. for 6 minutes.

My invention has been described in particular with reference to the back-coating of carpets and rugs with a frothed latex; however, my discovery may be profitably employed with and for the gellation of a wide variety of latex compositions coated upon porous support webs or mediums. For example, the use of open steam passed upwardly through a porous medium may be employed for the rapid gellation or curing of a frothed or regular latex coating on porous woven or non-woven fabrics, such as cotton, canvas, wool, etc., glass fiber mats or mineral wool Webs, asbestos, rayon, paper or the like. My invention provides a simple, inexpensive and improved method of obtaining gellation of frothed and other latices without the disadvantages of the prior art method.

What I claim is:

1. A method of preparing a gelled foam latex coated fibrous sheet material which method comprises;

applying a layer of a heat-gellable frothed latex composition onto one surface of a fibrous sheet material; applying live steam against the uncoated surface of said latex coated fibrous sheet material, the live steam under sutficient pressure to contact the surface of said sheet material and to cause the rapid progressive gellation of the latex layer from said one surface of the fibrous sheet toward the upper surface of the latex coating; and drying and curing the gelled latex layer. 2. The method of claim 1 which includes the additional step of: embossing a design into the gelled frothed latex layer; and curing and drying the embossed gelled latex layer.

3. The method of claim 1 wherein the latex composition comprises an elastomeric latex, a gelling agent, and a polymeric thickening agent.

4. The method of claim 1 wherein the fibrous sheet material is a tufted carpet having a woven backing fabric and a plurality of tufts on the face surface and a plurality of stitches on the back surface, and wherein the frothed latex is applied to the back surface of the carpet, and the steam applied against the downward face surface.

5. The method of claim 1 wherein the frothed latexcoated fibrous sheet material is passed over a steam box, said steam box constructed to direct steam admitted into the box to pass upwardly into contact with the underlying surface of said coated sheet material, the steam being admitted under suflicient pressure to how the said coated fibrous sheet material slightly upwardly as it passes over the box.

6. The method of claim 1 which includes directing radiant heat downwardly onto the upper surface of the frothed latex-coated fibrous sheet material to aid in the gelling of the latex layer.

7. A method of preparing a tufted rug having a skidresistant embossed cellular backing, the rug comprising a backing fabric with a plurality of tufts on the face which method comprises:

applying a layer of a frothed heat-gellable elastomeric latex composition onto the back surface of the rug;

directing live steam against the tufted face of the rug, the live steam under suflicient pressure to contact the face surface and to cause the rapid progressive gellation of the trothed latex layer on the back surface;

embossing a desired design into the gelled frothed latex layer; and

drying and curing the gelled embossed frothed latex layer.

8. The method of claim 7 wherein the frothed latex layer is gelled by passing the coated rug over the open top of a steam box, with the tufted face of the rug being substantially in contact with two sides of the box, and sufficient steam pressure being used to how the rug slightly upward as it passes over the open top of the steam box.

9. The method of claim 8 wherein radiant heat is directed downwardly onto the upper surface of the frothed latex layer.

10. The method of claim 7 wherein the gelled frothed layer is embossed by passing the gelled latex-coated rug under pressure through a pair of embossing rolls.

References Cited by the Examiner UNITED STATES PATENTS 2,590,849 4/1952 Dungler l171l9.8 X 2,817,597 12/1957 Alderfer 117-10 3,210,447 10/1965 Cyr et a1. 264-47 WILLIAM D. MARTIN, Primary Examiner.

H. W. MYLIUS, Assistant Examiner. 

1.
 1. A METHOD OF PREPARING A GELLED FOAM LATEX COATED FIBROUS SHEET MATERIAL WHICH METHOD COMPRISES: APPLYING A LAYER OF A HEAT-GELLABLE FROTHED LATEX COMPOSITION ONTO ONE SURFACE OF A FIBROUS SHEET MATERIAL; APPLYING LIVE STEAM AGAINST THE UNCOATED SURFACE OF SAID LATEX COATED FIBROUS SHEET MATERIAL, THE LIVE STEAM UNDER SUFFICIENT PRESSURE TO CONTACT THE SURFACE OF SAID SHEET MATERIAL AND TO CAUSE THE RAPID PROGRESSIVE GELLATION OF THE LATEX LAYER FROM SAID ONE SURFACE OF THE FIBROUS SHEET TOWARD THE UPPER SURFACE OF THE LATEX COATING; AND DRYING AND CURING THE GELLED LATEX LAYER. 